” many grids have the right to take your power from the batteries into the grid”
What you got to worry about in this scenario is the utility drains your batteries to 50% or less, without your knowledge, and the grid fails due to a storm. The whole purpose of the batteries YOU PURCHASED was to power your place and fridges in an outage. If your utility has ‘sucked you dry’ what then !!!?
You can disconnect your system from the grid at any time, by opening the main incoming breaker. They can’t bypass that.